A. Field of Invention
The present invention relates generally to detecting gamma radiation and more specifically to gamma camera systems.
B. Description of the Related Art
It is known in the art to use gamma cameras to create multi-dimensional images of the distribution of gamma emitting sources for applications including, but not limited to, medicine, astronomy, and detection of contraband. Current state of the art photon counting, large field-of-view, imaging gamma cameras utilize a plurality of photomultiplier tubes optically coupled to one side or edge of a scintillation crystal. The other side of the scintillation crystal is exposed to the radioactive source to be imaged via a gamma-ray collimator. When a gamma-ray photon interacts within the crystal, visible light is emitted by the crystal at the point of the interaction. This visible light from the interaction strikes many photomultiplier tubes (PMT's). The position of the gamma interaction is mathematically determined by analyzing the outputs of the photomultiplier tubes and is well known in the art. The energy deposited in the crystal by the incident gamma ray is proportional to the total amount of visible light emitted by the crystal. This is determined by integrating the outputs of the photomultiplier tubes, also well known in the art.
While known gamma cameras function well for their intended purpose, there are limitations. Some disadvantages in the known technology include, but are not limited to, the following. Photomultiplier tube performance tends to drift with temperature and time making frequent calibration necessary. Photomultiplier tube performance depends on their position within the earth's magnetic field. Determination of the position of an interaction is difficult because the detection area of the PMT is much larger than the size of the scintillation event or interaction, resulting in an image with low spatial resolution. Scintillation crystal exchange is difficult due to the direct optical coupling of the PMT's to the crystal. Therefore, what is needed are apparatus and methods that overcome the limitations of the prior art. The present invention overcomes one or more of the disadvantages of the prior art.